1. Field of the Invention
This invention relates to internal combustion engines and is particularly applicable to such engines of the Diesel or stratified charge type.
2. Description of the Prior Art
Despite their greater economy in amount and cost of fuel used, Diesel engines have made little headway in replacing spark-fired gasoline engines as the power unit of automobiles. This has been due largely to the relatively lower efficiency of existing Diesel engines on a power to weight ratio, their higher initial cost, lower maximum speed and special fuel requirements, without any offsetting advantage in noxious emissions. Heavy duty Diesel engines for other applications suffer from similar problems. It is believed that the greatest weakness of today's Diesel engine is its lack of an adequately effective fuel injection-ignition system.
Early Diesel engines utilized compressed air to vaporize and inject fuel into the combustion chambers at the top of the cylinders. This system worked well, but required multi-stage compressors to compress the air to from 800 to 1300 p.s.i., which added to the complexity, weight, power drain and cost of the engine. Consequently, manufacturers of modern Diesel engines have discarded air pressure fuel injection in favor of pressurized fuel injection systems, in which the required hydraulic pressure of several thousand p.s.i. on the fuel can be generated with less costly, heavy and power consuming equipment. But the "solid" pressurized fuel jet so produced does not produce as rapid and uniform burning of the fuel as would be desirable. Studies indicate that ignition tends to develop at the air-jet interface of the air envelope about the jet, with the fuel not yet adequately mixed with air, so that some ignition "pockets" are overrich in fuel and tend to generate smoke and odor due to insufficient oxidation, fuel cracking and carbonization. Other ignition pockets are too lean in fuel, tending to generate unburned hydrocarbons and odorous compounds. Both conditions impair engine performance, which ideally needs combustion at nearly a constant fuel-air ratio to the lean side of the stoichiometric, without delays due to erratic burning.
To alleviate these difficulties with pressurized fuel injection, it has been proposed, as in U.S. Pat. No. 2,046,003, to provide a cone of compressed air surrounding the jet as it passes into the combustion chamber, the compression being provided by individual pumps for each cylinder, operated by the cam shaft. The arrangements proposed have not been such as to provide compressed air at a pressure or temperature much above that prevailing in the combustion chamber. Adequacy and speed of combustion in the area surrounding the jet are possibly improved, but the internal, relatively "solid" area of the jet is not greatly effected, and this still gets ignited without adequate mixing with air.